Mold for fabricating optical fiber guide block

ABSTRACT

In a grindstone for fabricating a mold which has optical fiber engagement portions of an optical fiber guide block used for aligning optical fibers, two main grinding surfaces are provided to form the optical fiber engagement portions contacted with the sides of the optical fibers and a tip end portion which is contiguous to the two main grinding surfaces and which has a contour contained within a predetermined area. The predetermined area has a triangle shape which is defined by two tangent lines along the two main grinding surfaces and a preselected line drawn between two points determined on the two main grinding surfaces. The two points are decided in accordance with a predetermined formula.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a grindstone, a method of fabricatingmolds for fabricating optical fiber guide blocks, molds for fabricatingoptical fiber guide blocks, and an optical fiber guide block fabricationmethod, for the purpose of fabricating molds for fabricating opticalfiber guide blocks capable of holding and securing the ends of opticalfibers in a condition wherein their ends are positioned with highprecision and secured.

2. Description of the Related Art

Optical fiber guide blocks which have optical fiber engagement portionsare known as securing members for positioning and aligning multifibersat predetermined intervals with high location accuracy. In JapaneseUnexamined Patent Publications Nos. Hei 6-201936 [201936/1994] and Hei8-211244 [211244/1996], for example, optical fiber guide blocks aredisclosed which are obtained by forming glass in a hot press. InJapanese Unexamined Patent Publication No. Hei 6-94945 [94945/1994] isdisclosed an optical fiber guide block obtained by press-molding resin.

(1) In then past, the forming parts of optical fiber engagement portionsin molds have been formed by dividing the forming surfaces a number oftimes and grinding a little at a time with grindstones that are verysmall compared to the size of the work. With this method, in addition torequiring much time for the machining, it is very difficult to makemultifiber engagement portion forming, parts with high precision, and sothat the cross-sectional shape is always the same shape. As aconsequence, a shape is varied in configuration when observation is madeabout the perpendicular cross-sectional shape along the longitudinaldimension of one forming part, or when cross-sectional shapes ofdifferent forming parts are compared with each other.

(2) Also, in fabricating optical arrays, the optical fiber ends areengaged and lined up in optical fiber engagement portions in an opticalfiber guide block, and pressure blocks are used to press down on andsecure the optical fiber ends. In order to position and secure theoptical fiber ends with high location accuracy, it is necessary that theoptical fiber sides be supported, at two points by V-shaped opticalfiber engagement portions in the optical fiber guide block, in across-section seen from a direction perpendicular to the optical axis ofthe optical fiber ends secured, and at one point by the pressure surfaceof the pressure block. In the absence of such a three-point supportcondition, clearances (gaps) will develop between the sides of theoptical fiber, on the one hand, and the optical fiber engagementportions or the pressure surface of the pressure block, on the otherhand, making it very difficult to implement holding and securing withhigh location accuracy.

In order to perform optical fiber end securing by the three-pointsupport as described above, when an optical fiber is engaged in anoptical fiber engagement portion, not only must the optical fiberengagement portion exhibit a shape wherewith the optical fiber can bestably engaged, but the condition must be such as to permit a portion ofthe side of the optical fiber to expose its crown, standing away fromthe optical fiber engagement portion, without being imbedded in themiddle of the optical fiber engagement portion. In order to fabricateoptical fiber guide blocks having the shape described above bypress-molding, a specially shaped mold made to high precision isnecessary. Until now, however, no such mold, nor any method forfabricating such mold, has been known.

Furthermore, if the mold can align multifiber ends with a locationaccuracy within the allowable range, then, on an exceptional basis, acondition wherein optical fiber crown exposure cannot be effected ispermissible, but no such mold as this or method for fabricating suchmold as this is known either.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention is to provide agrindstone for fabricating molds for optical fiber guide blocks, afabrication method suitable for fabricating molds for fabricatingoptical fiber guide blocks for the purpose of fabricating optical fiberguide blocks by press-molding that make it possible to position andsecure optical fibers with high location accuracy for the purpose, offabricating molds for fabricating optical fiber guide blocks, and suchmolds, and also to provide a method for fabricating optical fiber guideblocks wherewith it is possible to position and secure optical fiberswith high location accuracy using the molds described in the foregoing.

It is another object of the present invention to provide a grindstonewherewith it is possible to position and align multifiber ends with highlocation accuracy within the allowable range, even in a conditionwherein the optical fibers are imbedded in the optical fiber engagementportions so that they cannot expose their crowns, a method offabricating molds for fabricating optical fiber guide blocks, and amethod of fabricating both molds for fabricating optical fiber guideblocks and the optical fiber guide blocks.

According to a first aspect of the present invention, there is provideda grindstone for fabricating a mold for molding by press-molding processat least the optical fiber engagement portions of an optical fiber guideblock that has optical fiber engagement portions for the purpose ofpositioning and aligning optical fibers at a fixed pitch; comprising:two main grinding surfaces that machine formed surfaces that support thesides of the optical fiber; and a shape wherein the angle θ subtended bythe two tangent lines which touch the two main grinding surfaces in across-section perpendicular to the main grinding surfaces constitutes anangle that is equal to or smaller than θc which satisfies therelationship noted below; and the contour of the tip that connects thetwo main grinding surfaces is contained within an area bounded by thetwo tangent lines and by a line that is tangent to an imaginary circleand perpendicular to the straight line connecting the intersection ofthe two tangent lines with the center of the imaginary circle, and thatpasses between the intersection and the center of the imaginary circle,when the imaginary circle, of radius Rmin as noted below, is inscribedin the area that is in the bight of the two tangent lines.

    θc=2 tan.sup.-1 {S.sup.2 -1)/2S}

where:

    Rmin=[RO+{RO/sin(θ/2)}-{YO/tan (θ/2)}]/[1-{1/sin(θ/2)}],

RO is the optical fiber radius, and

YO is half the pitch length of the optical fiber engagement portion.

According to a second aspect of the present invention, there is provideda grindstone for fabricating a mold for molding by press-molding processat least the optical fiber engagement portion(s) of an optical fiberguide block that has (a) groove-shaped optical fiber engagementportion(s) for the purpose of positioning optical fibers; comprising:two main grinding surfaces that machine formed surfaces that support thesides of the optical fiber; and a shape wherein the angle θ subtended bythe two tangent lines which touch the two main grinding surfaces in across-section perpendicular to the main grinding surfaces constitutes anangle that is not greater than θc which satisfies the relationship notedbelow; and the contour of the tip that connects the two main grindingsurfaces is contained within an area bounded by the two tangent linesand by a line that is tangent to an imaginary circle and perpendicularto the straight line connecting the intersection of the two tangentlines with the center of the imaginary circle, and that passes betweenthe intersection and the center of the imaginary circle, when theimaginary circle, of radius Rmin as noted below, is inscribed in thearea that is in the bight of the two tangent lines.

    θc=2 tan.sup.-1 {S.sup.2 -1)/2S}

where:

    Rmin=[RO+{RO/sin(θ/2)}-{YO/tan (θ/2)}]/[1-{1/sin(θ/2)}],

RO is the optical fiber radius, and

YO is the interval between the concavities when at least twogroove-shaped concavities are formed by the grindstone in a moldmaterial that is to be the mold, so as to form the optical fiberengagement portion(s) between the concavities.

The first aspect according to the present invention comprises opticalfiber engagement portions that position and align optical fibers at afixed pitch, with the restriction being that the optical fiberengagement portions are plural in number and arranged at equalintervals. The second aspect of the invention, however, comprisesgroove-shaped optical fiber engagement portions for the purpose ofpositioning the optical fibers, wherefore the optical fiber engagementportion may be singular in number, and also included are those which arenot arranged at equal intervals. When there is a single optical fiberengagement portion, there is no such concept as the pitch of the opticalfiber engagement portions. However, even with mold used where there is asingle optical fiber engagement portion, at least two B-2's must beformed in FIG. 8E, so the interval between the two B-2's is defined as2YO.

According to a third aspect of the present invention, there is provideda grindstone that, in the first and the second aspects of the presentinvention, has Rmin*, which satisfies the relationship noted below, inplace of Rmin.

    Rmin*=Rmin-(φ/5)

where:

φ is the optical fiber core diameter.

According to a fourth aspect of the present invention, there is provideda grindstone for fabricating a mold for molding by press-molding processat least the optical fiber engagement portions of an optical fiber guideblock that has optical fiber engagement portions for the purpose ofpositioning and aligning optical fibers at a fixed pitch; comprising:two main grinding surfaces that machine formed surfaces that support thesides of the optical fiber; wherein the angle θ subtended by the twotangent lines in a cross-section perpendicular to the main grindingsurfaces constitutes an aangle that exceeds θc which satisfies therelationship noted below.

    θc=2 tan.sup.-1 {(S.sup.2 -1)/2S}

where:

S=YO/RO,

RO is the optical fiber radius, and

YO is half the pitch length of the optical fiber engagement portion.

According to a fifth aspect of the present invention, there is provideda grindstone for fabricating a mold for molding by press-molding processat least the optical fiber engagement portion(s) of an optical fiberguide block that has (a) groove-shaped optical fiber engagementportion(s) for the purpose of positioning optical fibers; comprising:two main grinding surfaces that machine formed surfaces that support thesides of the optical fiber; wherein the angle θ subtended by the twotangent lines in a cross-section perpendicular to the main grindingsurfaces constitutes an angle that exceeds θc which satisfies therelationship noted below.

    θc=2 tan.sup.-1 {(S.sup.2 -1)/2S}

where:

S=YO/RO,

RO is the optical fiber radius, and

YO is the interval between the concavities when at least twogroove-shaped concavities are formed by the grindstone in a moldmaterial that is to be the mold, so as to form the optical fiberengagement portion(s) between the concavities.

According to a sixth aspect of the present invention, there is provideda method of fabricating a mold for fabricating an optical fiber guideblock; wherein the mold is for the purpose of molding by press-moldingprocess at least the optical fiber engagement portions of the opticalfiber guide block, the optical fiber guide block comprising: a pluralityof optical fiber engagement portions for the purpose of positioning andaligning optical fibers; comprising: a machining process for using agrindstone to grind a plurality of grooves in a mold material whichextend in the longitudinal dimension thereof; wherein the intervalbetween the grooves is made the forming part for the optical fiberengagement portions; and the contour of that portion of the forming partwhich forms the portions that are to support at least the optical fibersforms a portion of the contour shape of the grindstone.

If this method is employed, by performing grinding-machining so that aportion of the contour shape of the grindstone is formed in the shape ofthat portion of the cross-section of the optical fiber engagementportion forming parts that are to support the optical fiber, it ispossible to fabricate molds, with high productivity, so that thecross-sectional shapes of the multifiber engagement portion formingparts are the same. In other words, it is possible, using a singlegrindstone, to form grooves of the same shape in the mold material,based on the standard shape of the grindstone, and thereby to machinethe parts that form the optical fiber engagement portions. As aconsequence, it is possible to form multiple portions having the sameshape to a high precision, and to do this in an elegant manner.

According to a seventh aspect of the present invention, there isprovided a method of fabricating a mold for fabricating an optical fiberguide block, for the purpose of molding by press-molding process atleast the optical fiber engagement portions of the optical fiber guideblock; the optical fiber guide block comprising: (an) optical fiberengagement portion(s) for the purpose of positioning and aligningoptical fibers at a fixed pitch; wherein the grindstone of one of theaspects of the present inventions cited above, namely the first throughthe fifth invention, is used; and concavities extending in a prescribeddirection, of such depth that the intersection between the two tangentlines will be at a position deeper than dmin, as defined below, areformed, by a grinding process, on the flat surface of the mold material,at the pitch noted above, in a direction perpendicular to the prescribeddirection noted above, in a number that is the number of the opticalfiber engagement portions plus 1.

    dmin=[YO-RO·tan{(π-θ)/4}]/tan(θ/2)

According to an eighth aspect of the present invention, there isprovided a method of fabricating a mold for fabricating an optical fiberguide block, for the purpose of molding by press-molding process atleast the optical fiber engagement portions of said optical fiber guideblock; the optical fiber guide block comprising: (a) groove-shapedoptical fiber engagement portion(s) for the purpose of positioningoptical fibers; wherein the grindstone of one of the aspects of thepresent invention cited above, namely the first through the fifthaspects of the present invention, is used; and a plurality ofconcavities extending in a prescribed direction, of such depth that theintersection between the two tangent lines will be at a position deeperthan dmin, as defined below, are formed, by a grinding process, on theflat surface of the mold material, in a direction perpendicular to theprescribed direction noted above, and such that the interval between atleast two of these concavities becomes YO.

    dmin=[YO-RO·tan{(π-θ)/4}]/tan(θ/2)

According to a ninth aspect of the present invention, there is provideda method of fabricating a mold for fabricating an optical fiber guideblock, wherein in the seventh or eighth aspects of the presentinvention, concavities are machined at a depth such that theintersection between the two tangent lines becomes a position that isshallower than dmax, as defined below.

    dmax=YO/tan(θ/2)

According to a tenth aspect of the present invention, there is provideda method of fabricating a mold for fabricating an optical fiber guideblock, comprising: a process for machining such that, aftergrinding-machining the concavities of the seventh, eighth, or ninthaspect of the present invention, outside of the two grooves positionedoutermost among the grooves, the portions which connect to the bottomsof at least those two grooves are in the same plane as the bottoms ofthose two grooves.

According to an eleventh aspect of the present invention, there isprovided a mold for fabricating an optical fiber guide block that hasbeen fabricated by one of the methods cited in the sixth through thetenth aspects of the present invention.

According to a twelfth aspect of the present invention, there isprovided a mold for fabricating an optical fiber guide block, for thepurpose of molding, by press-molding process, at least the optical fiberengagement portions of an optical fiber guide block comprising opticalfiber engagement portions for the purpose of positioning and aligningoptical fibers at a fixed pitch: comprising: a plurality of concavitiesthat extend in one direction in the forming surface; wherein: thetangent lines at the points where the portions that are to support theoptical fiber at the two sloping surfaces which configure theconcavities, in a cross-section that is perpendicular to thelongitudinal dimension of the concavities, subtend an angle θ that isequal to or smaller than θc which satisfies the relationship notedbelow; the perpendicular cross-sectional shape of the concavities issuch that the contour thereof is contained within an area bounded by thetwo tangent lines that touch the sloping surfaces and by a line that istangent to an imaginary circle and perpendicular to the straight lineconnecting the intersection of the two tangent lines with the center ofthe imaginary circle, and that passes between the intersection and thecenter of the imaginary circle, when the imaginary circle, of radiusRmin as defined below, is inscribed in the area that is in the bight ofthe two tangent lines; the depth of the concavities is such that theintersection of the two tangent lines is at a position deeper than dmin,as defined below; and the forming surfaces between the concavities arewhat form the optical fiber engagement portions.

    θc=2 tan.sup.-1 {S.sup.2 -1)/2S}

where:

S=YO/RO,

    Rmin=[RO+{RO/sin(θ/2)}-{YO/tan (θ/2)}]/[1-{1/sin(θ/2)}],

    dmin=[YO-RO·tan{(π-θ)/4}]/tan(θ/2),

RO is the optical fiber radius, and

YO is half the pitch length of the optical fiber engagement portion.

According to a thirteenth aspect of the present invention, there isprovided the mold for fabricating an optical fiber guide block in thetwelfth aspect of the present invention, wherein the cross-sectionalshapes perpendicular to the longitudinal dimension of a plurality ofconcavities are the same.

According to a fourteenth aspect of the present invention, there isprovided a mold for fabricating an optical fiber guide block, for thepurpose of molding, by press-molding process, at least the optical fiberengagement portions of an optical fiber guide block that comprisesgroove-shaped optical fiber engagement portions for the purpose ofpositioning optical fibers; comprising: convexities that extend in thelongitudinal dimension of the forming surface; and concavities thatextend in the longitudinal dimension, arrayed with the convexitiessandwiched in between them; wherein: the tangent lines at the pointswhere are formed the portions of the two sloping surfaces that configurethe concavities in a cross-section perpendicular to the longitudinaldimension of the concavities, which portions are to support the opticalfibers, subtend an angle θ that is equal to or smaller than θc whichsatisfies the relationship noted below; the perpendicularcross-sectional shape of the concavity or concavities is such that thecontour thereof is contained within an area bounded by the two tangentlines that touch the sloping surfaces and by a line that is tangent toan imaginary circle andperpendicular to the straight line connecting theintersection of the two tangent lines with the center of the imaginarycircle, and that passes between the intersection and the center of theimaginary circle, when the imaginary circle, of radius Rmin as definedbelow, is inscribed in the area that is in the bight of the two tangentlines; the depth of the concavities is such that the intersection of thetwo tangent lines is at a position deeper than dmin, as defined below;and one or other of the sloping surfaces that form the concavity orconcavities is what forms the surface(s) that support(s) the opticalfibers in the optical fiber engagement portion(s).

    θc=2 tan.sup.-1 {S.sup.2 -1)/2S}

where:

YO/RO,

    Rmin=[RO+{RO/sin(θ/2)}-{YO/tan (θ/2)}[/1-{1/sin(θ/2)}],

    dmin=(YO-RO·tan{(π-θ)/4}]/tan(θ/2),

RO is the optical fiber radius, and

2YO is the interval between the concavities arrayed so as to sandwichthe convexities between them.

According to a fifteenth aspect of the present invention, there isprovided the mold for fabricating an optical fiber guide block in thefourteenth aspect of the present invention, wherein the cross-sectionalshapes perpendicular to the longitudinal dimension of the concavity orconcavities are the same.

According toasixteenth aspect of the present invention, there isprovided the mold for fabricating an optical fiber guide block in thetwelfth through the fifteenth aspects of the present invention, having,in place of Rmin, Rmin* which satisfies the relationship noted below.

    Rmin*=Rmin-(φ/5)

where:

φ is the optical fiber core diameter.

According to a seventeenth aspect of the present invention, there isprovided a mold for fabricating an optical fiber guide block, for thepurpose of molding, by press-molding process, at least the optical fiberengagement portions of an optical fiber guide block comprising opticalfiber engagement portions for the purpose of positioning and aligningoptical fibers at a fixed pitch; comprising: a plurality of concavitiesthat extend in one direction in the forming surface; wherein: thetangent lines at the points where the portions that are to support theoptical fiber at the two sloping surfaces which configure theconcavities, in a cross-section that is perpendicular to thelongitudinal dimension of the concavities, subtend an angle θ thatexceeds θc which satisfies the relationship noted below; the depth ofthe concavities is such that the intersection of the tangent lines is ata position deeper than dmin, as defined below; and the forming surfacesbetween the concavities are what forms the optical fiber engagementportions.

    θc=2 tan.sup.-1 {S.sup.2 -1)/2S}

where:

S=YO/RO,

    dmin=[YO-RO·tan{(π-θ)/4}]/tan(θ/2),

RO is the optical fiber radius, and

YO is half the pitch length of the optical fiber engagement portion.

According to an eighteenth aspect of the present invention, there isprovided the mold for fabricating an optical fiber guide block in theseventeenth aspect of the present invention, wherein the cross-sectionalshapes perpendicular to the longitudinal dimension of a plurality ofconcavities are the same.

According to a nineteenth aspect of the present invention, there isprovided a mold for fabricating an optical fiber guide block, for thepurpose of molding, by press-molding process, at least the optical fiberengagement portions of an optical fiber guide block that comprisesgroove-shaped optical fiber engagement portions for the purpose ofpositioning and supporting optical fibers; comprising: convexities thatextend in the longitudinal dimension of the forming surface; andconcavities that extend in the longitudinal dimension, arrayed with theconvexities sandwiched in between them; wherein: the tangent lines atthe points where are formed the portions of the two sloping surfacesthat configure the concavities in a cross-section perpendicular to thelongitudinal dimension of the concavities, which portions are to supportthe optical fibers, subtend an angle θ that exceeds θc which satisfiesthe relationship noted below; the depth of the concavities is such thatthe intersection of the tangent lines is at a position deeper than dmin,as defined below; and one or other of the sloping surfaces that form theconcavity or concavities is what forms the surface(s) that support(s)the optical fibers in the optical fiber engagement portion(s).

    θc=2 tan.sup.-1 {S.sup.2 -1)/2S}

where:

S=YO/RO,

    dmin=[YO-RO·tan{(π-θ)/4}]/tan(θ/2),

RO is the optical fiber radius, and

2YO is the interval between the concavities arrayed so as to sandwichthe convexities between them.

According to a twentieth aspect of the present invention, there isprovided the mold for fabricating an optical fiber guide block in thenineteenth aspect of the present invention, wherein the cross-sectionalshapes perpendicular to the longitudinal dimension of the concavity orconcavities are the same.

According to a twenty-first aspect of the present invention, there isprovided the mold for fabricating an optical fiber guide block in thetwelfth through the twentieth aspect of the present invention, whereinthe shapes of the bottoms of the concavities in a cross-sectionperpendicular to the longitudinal dimension of the concavities are thesame.

According to a twenth-second aspect of the present invention, there isprovided the mold for fabricating an optical fiber guide block in thetwelfth through the twentieth aspects of the present invention, whereinthe bottoms of the concavities are flat.

According to a twenty-third aspect of the present invention, there isprovided the mold for fabricating an optical fiber guide block in thetwelfth through the twenty-second invention, comprising: a plurality ofconcavities, wherein: the forming surfaces bounded between theconcavities are flat; and the flat surfaces are positioned in the sameplane.

According to a twenty-fourth aspect of the present invention, there isprovided the mold for fabricating an optical fiber guide block in thetwelfth through the twenty-third aspects of the present invention,having a mold release thin film(s), at least on the forming surface.

According to a twenth-fifth aspect of the present invention, there isprovided a method of fabricating optical fiber guide blocks wherein: amold for fabricating an optical fiber guide block in the twelfth throughthe twenty-fourth aspects of the present inventions is used; and the rawmaterial to be molded is press-molded under heat.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view describing the correlations between themold, grindstone, optical fiber, and optical fiber guide blockindicating the optical fiber crown exposure conditions according to anembodiment of the present invention;

FIGS. 2A through 2D are a set of cross-sectional views describing thetip shape of grindstones according to the embodiment, FIGS. 2A and 2Bdepicting circular arc shapes, and FIGS. 2C and 2D depicting flatshapes;

FIGS. 3A through 3C are a set of descriptive drawings of a mold,grindstone, and optical fiber guide block according to the embodiment,FIG. 3A being a cross-sectional view of a mold for molding optical fiberengagement portions, FIG. 3B being a view, seen as a cross-sectionperpendicular to the optical axis of optical fiber, of the vicinity ofoptical fiber engagement portions in an optical fiber guide block in acondition wherein optical fibers are engaged in the optical fiberengagement portions, and FIG. 3C being a view, seen in the perpendicularcross-section noted above, of a condition wherein optical fibers areengaged and aligned in V-shaped optical fiber engagement portions in anoptical fiber guide block C;

FIGS. 4A through 4C are an explanatory diagram that represents theheight relationship between the intersection and the optical fibercrowns in optical fiber engagement portions as the value of the angle θsubtended by the tangent lines in the main grinding surfaces of thegrindstone according to the embodiment is changed, FIG. 4A being across-sectional view for θ<θc, FIG. 4B being a cross-sectional view forθ=θc, and FIG. 4C being a-cross-sectional view for θ>θc;

FIG. 5 is a cross-sectional view of the vicinity of concavities in amold according to the embodiment when θ=θc;

FIG. 6 is an-explanatory diagram for deriving Rmax according to theembodiment;

FIGS. 7A, 7B, 7C, 7D and 7E are a set of diagonal views depictingmachining processes for fabricating a mold from a mold material bygrinding with a grindstone according to the embodiment;

FIGS. 8A, 8B, 8C, 8D and 8E are a set of cross-sectional viewscorresponding to the processes depicted by the diagonal views in FIGS.7A through 7E;

FIGS. 9A and 9B are general explanatory diagrams of grindstonesaccording to the embodiment;

FIG. 10 is an explanatory diagram for deriving dmin according to theembodiment;

FIGS. 11A through 11C are explanatory diagrams of two-sided machiningaccording to the embodiment, FIG. 11A depicting ideal two-sidedmachining, FIG. 11B depicting machining wherewith positioning isimpossible, and FIG. 11C depicting two-sided machining in a case wherethe bottoms of the concavities in the mold are flat;

FIGS. 12A through 12C are a set of cross-sectional views of moldsaccording to the embodiment when the depth of the intersection A-4 ischanged, FIG. 12A being when d=dmin, FIG. 12B when dmin<d<dmax, and FIG.12C when d=dmax;

FIG. 13 is a cross-sectional view of the vicinity of, optical fiberengagement portions according to another embodiment, wherein theexpanded range Rmin*≦R≦Rmin applies;

FIGS. 14A and 14B are a pair of cross-sectional views of moldscorresponding to Embodiment 1, with FIG. 14A diagramming the case whereR>Rmin, and FIG. 14B the case where R=Rmax;

FIGS. 15A and 15B are a pair of cross-sectional views of moldscorresponding to Embodiment 2, with FIG. 15A diagramming the case whereW=2WR, and FIG. 15B the case where W is made maximum;

FIG. 16 is a diagonal view of an optical fiber guide block according toEmbodiment 3;

FIGS. 17A and 17B are a set of explanatory diagrams for an optical fiberarray according to Embodiment 3, FIG. 17A being a diagonal view, andFIG. 17B being a front elevation; and

FIGS. 18A through 18D are a set of process drawings which describe amethod of fabricating an optical fiber guide block with a mold forpress-molding according to Embodiment 3, FIG. 18A being a frontcross-sectional view of the front of the press, FIG. 18B a sidecross-sectional view thereof, FIG. 18C a front cross-sectional view ofthe middle of the press, and FIG. 18D a side cross-sectional viewthereof.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will now be described specifically, using drawingsas appropriate. Before that, however, the main parameters of the presentinvention will be briefly listed.

(1) Rmin is a crown-exposure condition

(2) dmin is a condition for two-point support by an optical fiberengagement portion

(3) when θ<θc, the grindstone tip shape becomes a problem

(4) when Rmax is exceeded, θ cannot be guaranteed (when shape ofgrindstone tip is a circular arc)

(5) when dmax is exceeded, the mold becomes sharply pointed andbreakable

(6) Rmin≦R≦Rmax is to hold true.

In FIG. 3C diagrammed a condition wherein optical fibers F are engagedand aligned in V-shaped optical fiber engagement portions C-1 in anoptical fiber guide block C, as viewed in a cross-section that isperpendicular to the optical axis of the optical fiber. In FIG. 3B isdepicted the vicinity of the optical fiber engagement portions in anoptical fiber guide block in a condition wherein optical fibers are notengaged in the optical fiber engagement portions. And in FIG. 3A isgiven a cross-section of a mold B for molding the optical fiberengagement portions diagrammed in FIG. 3B. Here the concavities B-2 ofthe mold B are formed by grinding-machining using a grindstone A. Thisgrindstone A comprises two main grinding surfaces A-1 which machine theforming surfaces B-0 (including points B-4) that form the surfaces thatcontain the points C-2 which support the optical fiber sides F-1. Themain grinding surfaces A-1 grind the two sloping surfaces B-3 which formthe concavities B-2 of the mold B in FIG. 3A. In a cross-section (in aplane parallel to the plane of the page) that is perpendicular to thetwo main grinding surfaces A-1 of the grindstone A, the angle subtendedby the two main grinding surfaces A-1 is designated as θ.

FIGS. 4A through 4C diagram the height relationship between theintersection A-4 and the crowns of the optical fibers F in the opticalfiber engagement portions C-1 as the angle θ subtended by the maingrinding surfaces A-1 is changed. If we define θ=θc as the anglesubtended when the crowns of the optical fibers F and the intersectionA-4 coincide (FIG. 4B), then, when θ<θc, the optical fibers F will befurther imbedded than the position of the intersection A-4 (FIG. 4A),and when θ>θc, they will emerge (FIG. 4C). The relational formula forthe angle θc is given below.

    θc=2 tan.sup.-1 {(S.sup.2 -1)/2S}

where S=YO/RO,

RO is the optical fiber radius, and

YO is half the optical fiber engagement portion pitch length. Thisformula is readily derived from FIG. 5, which diagrams a cross-sectionof the vicinity of the concavities in the mold B with θ=θc.

    When θ<θc                                      (1)

When a grindstone A wherein the angle θ is less than θc, satisfying therelational equation (1) above, is used, it is expedient to posit twotangent lines A-2 which, as depicted in FIG. 1, touch the main grindingsurfaces A-1, and toge ther subtend an angle θ in a cross-sectionperpendicular to the two main grinding surfaces A-1. The two tangentlines A-2 cross at the intersection A-4. Now, in the region betweenthese two tangent lines A-1, a condition is supposed wherein animaginary circle A-3-1 having radius Rmin, as defined below, isinscribed. Rmin is the minimum radius of curvature for the tip of thegrindstone necessary for the optical fiber crown exposure.

    Rmin=[RO+{RO/sin(θ/2)}-{YO/tan (θ/2)}]/[1-{1/sin(θ/2)}](2)

This formula (2) defines a critical condition for the crown exposure ofthe optical fibers F. It can be derived from the cross-sectional view ofthe mold in FIG. 1.

We next suppose a straight line A-6 that connects the intersection A-4between the two tangent lines A-2 and the center A-5-1 of the imaginarycircle A-3-1, and a tangent line A-7-1 of the imaginary circle A-3-1that is perpendicular to the straight line A-6 and that passes betweenthe intersection A-4 and the center A-5-1 of the imaginary circle A-3-1.The portion where the two main grinding surfaces A-1 connect in thecross-section of the grindstone A perpendicular to the two main grindingsurfaces A-1 will be called the tip of the grindstone A, but thegrindstone A that is used has a shape that comprises the contour of thistip within the area bounded by the two tangent lines A-2 and the tangentline A-7-1. This is for the purpose of exposing the crowns of theoptical fibers F. More specifically, the grindstone A that is usedcontains the outline of the tip within the region (including theboundaries thereof) bounded, in FIG. 1, by the straight line A-2-c thatconnects the points A-2-a and A-2-b, the two tangent lines A-2, and thetangent line A-7-1 (the cross-hatched region in FIG. 1). Suchgrindstones A include those wherein the cross-sectional shape describedis such that the cross-section of the tip is a circular arc A-10, asdiagrammed in FIGS. 2A and 2B, and wherein it is such that the tip isflat, as at A-11, as diagrammed in FIGS. 2C and 2D.

When the grindstone tip has a cross-sectional shape that is defined by acircular arc, the aforementioned conditions relative to the grindstonetip shape can be expressed in different terms, as follows. A conditionis supposed wherein an imaginary circle A-3-2 of radius Rmax, as definedbelow, is inscribed in the area bounded by the two tangent lines A-2, asdiagrammed in FIG. 1. Rmax is the maximum radius of curvature for thegrindstone tip that can guarantee θ.

    Rmax={YO-RO cos(θc/2)}/cos(θc/2)               (3)

This formula indicates the radius of the circle A-3-2 that touches acircle of radius RO at the tangent line A-2. Its derivation may beunderstood from FIG. 6 which diagrams a cross-section of the mold.

In order to expose the crowns of the optical fibers F while guaranteeingθ, it is necessary that the radius of curvature of the grindstone tipsatisfy the expression Rmin≦R≦Rmax.

A process wherein a grindstone A of such a shape is used to fabricate,by grinding-machining, a mold B, from a mold material, will now bedescribed. FIGS. 7A through 7E provide diagonal views of the machiningprocess. FIGS. 8A through 8E provide corresponding cross-sectional viewsof the process depicted in the diagonal views. First a concavity B-2 isground by a grindstone A of the shape noted above, in the flat surfaceB-1 of a mold materialsB (FIGS. 7A and 7B). At this time, the depth ofthe concavity B-2 is made such that the position of the intersection A-4is a position that is deeper than dmin, defined below, so that theoptical fiber sides F-1 will be supported at two points by the opticalfiber engagement portions C-1 of the optical fiber guide block C (FIG.8E). This is to provide two-point support.

    dmin=[YO-RO·tan{(π-θ)/4}]/tan(θ/2) (4)

This formula (4) is easily derived from FIG. 10 which represents thecase where d=dmin, the condition necessary for the optical fiber F totouch the bottom of the concavity B-2 of the mold B.

The concavities B-2 are formed so that each extends in the longitudinaldimension, as depicted in FIGS. 7B and 7C, and these are formed in adirection that is perpendicular to the longitudinal direction, with apitch interval 2YO, in a number that is the number of optical fiberengagement portions to be formed plus 1, and such that the depth betweenthe concavities B-2 is constant (FIGS. 7D and 7E). The point of formingthese in a number that is the number of optical fiber engagementportions plus 1 will be explained subsequently with reference to FIGS.11A through 11C.

    When θ>θc                                      (2)

When angle θ exceeds θc, as diagrammed in FIG. 4C, the shape of the tipof the grindstone A may be pointed, or described by a circular arc, orflat, orsome other shape. That is because then the crown exposure willbe guaranteed irrespective of the tip shape. The method of using agrindstone A shaped in this manner to form concavities B-2 in a moldmaterial B-1 is the. same as the method described above. However, theintersection A-4 between the tangent lines A-2 that are the two tangentlines of the main grinding surfaces A-1 in a cross-section perpendicularto the two main grinding surfaces A-1 of the grindstone A, as diagrammedin FIG. 1, is also supposed for the range wherein θ>θc, and the depth ofthe concavities B-2 in the mold B is made to be at a deeper positionthan the intersection A-4.

Irrespective of the angle θ, the cross-sectional shape of theconcavities B-2 will reflect the cross-sectional shape of the grindstoneA used for grinding. More specifically, the angle that is subtended bythe tangent line of the mold contour at a point B-4 which forms a placeC-2 that supports the optical fiber F diagrammed in FIG. 3C, and,similarly, by the tangent line of the mold contour at the neighboringpoint B-4, equals θ.

The depth of the concavities B-2, moreover, is made such that theintersection A-4 is deeper than dmin, and shallower than dmax, definedbelow.

    dmax=YO/tan(θ/2)                                     (5)

This formula (5) is easily derived from FIG. 12C which diagrams the casewhere d=dmax, which is the condition necessary for the flat bottom todisappear from the engagement portions C-1 of the optical fiber guideblock C.

By making it so that the intersection A-4 is at a position that isshallower than dmax, some of the surface B-1 will remain between theconcavities B-2 because the surface B-1 (surface wherein the concavitiesare ground) of the mold material depicted in FIGS. 7A through 7E isflat.

When optical fiber engagement portions C-1 are formed in an opticalfiber guide block C using such a mold B as this, what is obtained is anoptical fiber guide block C wherein the bottoms of the optical fiberengagement portions C-1 are comprised of flat surfaces (FIGS. 3B and3C).

The grindstones A of the present invention are mainly used asgrindstones which are turned, as represented in FIGS. 7A through 7E. Inorder to machine the desired mold using the grindstone in this manner,it is necessary:

(1) that the grindstone have a turning shaft; and

(2) that either the main grinding surfaces form symetrical turningsurfaces each of which are centered on a turning shaft, or that theshape thereof be such that imaginary symmetrical turning surfaces calibe circumscribed about the main grinding surfaces when the axis ofsymmetry is made to coincide with the turning axis of the grindstone.

Diagramming this yields FIG. 9A. In this figure, at points h, i, and j,etc., about the periphery of the grindstone, in the grindstones A thatare set forth in the first through the fifth invention, the maingrinding surface p constitutes a symmetrical turning surface, relativeto axis X, in the periphery of the grindstone. However, this does notmean that machining cannot be performed unless it is with a grindstone Ahaving symmetrical turning surfaces, as in FIG. 9A. In some cases itwill be possible to perform the machining even if, as in FIG. 9B, aconcavity e is made in the periphery, or a groove g is made in the maingrinding surface p, or a chip k develops. That being so, the grindstonesA of the present invention include those having shapes as in FIG. 9B, solong as, taking the main grinding surface p in FIG. 9A as an imaginarysymmetrical turning surface, the grindstone A is such that it cancircumscribe such imaginary surface.

By the main grinding surface p, moreover, is meant a surface that, ofthe surfaces of the grindstone A, is primarily used in grinding. Thereis no problem with having a projection u in a portion not used ingrinding, as depicted in FIG. 9B. In such case, the portion with theprojection u is rendered so that it is not contained in the maingrinding surface p.

Embodiments of the present invention will now be described.

    Rmin≦R≦Rmax                                  (1)

Grinding machining is performed, while turning a grindstone A,perpendicularly to the surface B-1 of a mold material B, as diagrammedin FIGS. 7A through 7E, so that, taking the surface of the mold materialas the reference, the depth is made so that the intersection A-4diagrammed in FIG. 1 is at a position which is deeper than dmin, aspreviously defined. After forming a concavity B-2 extending in thelongitudinal dimension while moving the grindstone A as depicted in thedrawing, the relative positions of the grindstone A and the moldmaterial B are shifted in a direction perpendicular to the longitudinaldirection by a pitch of 2YO, and grinding is again done with thegrindstone A, so that the depth becomes the same as was formedpreviously, and so that the concavity B-2 foried previously isparalleled. This process is done repeatedly to grind-machine concavitiesB-2 in a number equal to the number of optical fiber engagement portionswhich are to be fabricated by press-molding process plus 1.

It is preferable that the mold material B here have the anti-oxidationproperties required for use in press-molding glass, that it benon-reactive with glass, and that it exhibit neither morphological norplastic change in a high-temperature environment. Silicon carbide,tungsten carbide, alumina, zirconia, crystalline glass, silicon, andcermets of titanium carbide and titanium nitride, etc., may be listed asspecific materials. As to the grindstone A for grinding these moldmaterials B, it may be a resin-bonded diamond-grindstone or ametal-bonded diamond grindstone or the like. The grinding process notedabove may be performed with a dicing machine or other grinding-machiningapparatus used for precision machining.

To add some points here to what has already been said about the shape ofthe grindstone A, circular arc shapes, flat shapes, and parabolic shapesmay be mentioned specifically as shapes for the cross-section of the tipthereof. If the shape is that of a circular arc, or flat, then not onlywill the grindstone fabrication be comparatively easy, but there will belittle degradation in the shape of the tip due to wear, as compared togrindstones having a pointed tip, and the grinding-machining of thewhole shape can be done stably.

When the angle θ is equal to or smaller than θc, then, as diagrammed inFIGS. 4A through 4C, if the cross-sectional shape of the grindstone tipis not contained within the area described earlier, press-moldirigprocess cannot be performed wherewith optical fiber F crown exposure ispossible. When, on the other hand, the angle θ is larger than θc, thenoptical fiber F crown exposure becomes independent of thecross-sectional shape of the tip of the grindstone A that is used. Inother words, even if a grindstone having a sharp tip is used, a mold Bcan be obtained for forming an optical fiber guide block C wherewithcrown exposure of the optical fiber F is possible.

The depth to which the concavities B-2 are ground, that is, the depth ofthe concavities B-2 of the mold B, must be such that the intersectiondiagrammed in FIG. 1 is at a position which is deeper than dmin definedearlier. When the position of that intersection A-4 is at dmin orshallower than dmin, then, when an optical fiber F is engaged in anoptical fiber engagement portion C-1, the optical fiber F will come incontact with the bottom of the optical fiber engagement portion C-1, theoptical fiber F will be pushed up from the two support points of theoptical fiber engagement portion C-1, and it will cease to be possibleto restrain the position of the optical fiber F in the direction inwhich the optical fibers F are aligned. When the optical fibers F areengaged and aligned in the optical fiber engagement portions C-1 by amold B that satisfies the conditions noted above, the crown exposure ofeach optical fiber F is possible, and an optical fiber guide block C isobtained wherein the optical fibers F are stably engaged in the opticalfiber engagement portions C-1.

The optical fibers F are engaged and aligned in these optical fiberengagement portions C-1, the side surfaces of the crown-exposed opticalfibers are pressed down under the pressing surface of a pressure block,and bonded and secured. In this condition, an optical fiber array isobtained wherein the optical fiber sides are supported at three points,namely at two points by the optical fiber engagement portions, and atone point by the pressing surface of the pressure block, looking at across-section perpendicular to the optical axes of the optical fibers.The light input/output end surfaces of this optical fiber array areoptically polished and made ready for actual use.

When the cross-section of the grindstone tip is shaped as a circulararc, if the radius of curvature R of the circular arc increases, and theapex of the grindstone tip moves outside of the straight line A-2-c,outside of the region bounded by the tangent lines A-2, the straightline A-7-1, and the straight line A-2-c, as diagrammed in FIG. 1, thenthe points C-2 (which are points on the optical fiber guide block C thatcorrespond to points A-2-a and A-2-b in FIG. 1) at which are supportedthe optical fiber sides F-1 in the optical fiber guide block C in FIG.3A through 3C cease to be positioned on the main grinding surfaces A-1.In other words, the angles subtended by the tangent lines on thecross-sectional contour of the optical fiber engagement portions C-1 atpoint C-2, and by the tangent lines on the contour of the formingsurfaces B-0 in the mold B that forms the points C-2, cease to be theangle θ subtended by the two tangent lines A-2 that touch the maingrinding surfaces of the grindstone.

Now, to explain further about the grinding depth of the concavities B-2,it is desirable that the grinding depth, that is, the depth of theconcavities B-2, be such that the intersection A-4 in FIG. 1 be at aposition that is shallower than dmax, defined earlier. The reason isthat, because the surface of the mold material B in, which theconcavities are ground is flat, when the grinding depth is made as notedabove, some of the flat surface B-1 of the mold material B remains as aforming surface sandwiched between the concavities B-2. In such a mold Bas this, the spaces between the concavities B-2 are flat and have noedges which are sharp or thin, wherefore there is no danger of the tipsof the concavities B-2 in the mold B being chipped, thus making the moldB easy to handle. If, on the other hand, the depth of the concavities ismade deeper than dmax, defined earlier, then sharp and thin edges areproduced between the concavities which readily chip and easily lead toproblems. When press-molding an optical fiber guide block C, such a moldB as this forms flat surfaces at the bottom of the optical fiberengagement portions C-1. In glass press-molding process that forms flatbottoms like this, after the optical fiber engagement portions C-1 areformed, the stresses that are produced in the tips between theconcavities of the mold and in the bottoms of the optical fiberengagement portions C-1 are dispersed in a cooling process, whichfunctions to reduce chipping and cracking in the tips between theconcavities in the die.

After subjecting the mold material B to the concavity grinding process,the portions B-5 that are outside of the concavities B-2-1 and B-2-2that are positioned outermost among the plurality of concavities B-2, inFIG. 11A, and that are connected at least with the bottoms of theoutermost concavities B-2-1 and B-2-2, are machined so that they arebrought into the same plane B-6 as the bottoms of the concavities B-2-1and B-2-2 ((1) concavity machining→(2) ideal machining→(3) mold).

This process is hereinafter called two-sided machining. By thistwo-sided machining, a mold is obtained having a shape such that theportions on both sides of the mold and the bottom of the concavities B-2are positioned in the same plane B-6.

In an optical fiber array comprising an optical fiber guide block C thatis press-formed by such a mold B as this, a pressure block, and opticalfibers, the gap between the bonding surfaces of the optical fiber guideblock C and pressure block can be made uniform at every place.

However, in cases where the bottoms of the concavities in the mold B arenot flat (when the grindstone tip shape is made sharp), when performingthe two-sided machining, if the positions of the centers of theoutermost concavity bottoms B-2-1 and B-2-2 and the ends of the portionsremoved by the two-sided machining are not accurately positioned, anunwanted non-machined portion having the shape of a projection B-7, asdiagrammed in FIG. 11B, will be made. When, however, the bottom of theconcavities in the mold B are made flat (when the grindstone tip shapeis made flat), then, as diagrammed in FIG. 11C, the positioningprecision tolerance can be made as large as the width of the flat bottomof the concavity B-2, so there will be no remaining unmachined portionhaving the shape of the projection B-7 due to a positioning error. Thetwo-sided machining can be performed accurately by using a dicingmachine or other precision machining apparatus in doing the grinding.

After shape-machining the mold as described in the foregoing, a moldrelease thin film(s) is formed, at least on the forming surfaces B-0 ofthe mold, to facilitate post-formation die separation of the objectbeing press-formed. The mold release thin film(s) may be carbon-based orplatinum alloy-based, etc.

Molds such as this are used to press-form the material being formed, ata press-formable temperature. Using such molds as this, for example, adown die is formed integrally by taking such a mold and another mold forforming the pedestal of an optical fiber guide block for holding anoptical fiber sheath and securing these in a frame, using trunk dies andan up die, placing the material to be formed in the space bounded by thedown die, trunk dies, and up die, and conducting press-molding at apress-formable temperature. Optical fiber engagement portions are thusformed in the glass that is formed, and an optical fiber guide block isobtained.

The molds of the present invention are not limited to examples in whichan optical fiber guide block such as noted above is used. Opticalcomponent mounting boards and optical component securing hardware, etc.,used in precisely positioning light-emitting devices or light-sensingdevices, in addition to optical fibers, can be employed in forming theoptical fiber engagement portions.

Any glass that is press-formable can be used as the glass to be formed.However, glass having a low coefficient of thermal expansion, a yieldpoint below 600°, and outstanding UV transmissivity is desired. Glassescontaining SiO₂, B₂ O₃, and ZnO, for example, may be recommended. Anyother commercially sold press glass may be used.

The values for YO and RO arrived at by making compensations based on themean coefficient of thermal expansion between the glass transitiontemperature and the room temperature of the mold material and the glassthat are press-formed during mold fabrication.

    Rmin*≦R≦Rmax                                 (2)

Now, in describing the embodiment set forth in the foregoing, it ispresupposed that, unless the three-point support condition is satisfied,the sides of the optical fiber ends will develop clearance (gaps)between the optical fiber engagement portions or with the pressingsurface of the pressure block, making it very difficult to effectholding and securing with high location accuracy. In actuality, however,it has been found that, even in a condition wherein the optical fibersare embedded inside the optical fiber engagement portions so that crownexposure can no longer be effected, if the range of the radius ofcurvature R of the grindstone A is expanded as noted below, lightconnection losses can be kept within allowable limits when an opticalfiber array is used in a condition wherein crown exposure can no longerbe effected.

    When θ≦θc                               (a)

    Rmin*=Rmin-(φ/5)                                       (6)

In the range where Rmin<R≦Rmax, when optical fibers are engaged andpositioned in optical fiber engagement portions in a crown-exposedcondition, and the optical fibers are pressed down with a pressureblock, the optical axes of the optical fibers are aligned on a straightline in a cross-section perpendicular to the optical axes.

In the expanded range Rmin*≦R≦Rmin, the amount of optical fiber crownexposure Δ will be Δ≦0. In this condition, when the optical fiberengagement portions C-1 are covered with a pressure block M, asdiagrammed in FIG. 13, each of the plurality of optical fibers F will besecured in one of the positions where it is restrained within a rangebounded by the pressing surface M-1 of the pressure block M and theoptical fiber engagement portion C-1. Because the crown-exposure amountΔ is Δ≦0, however, the optical axes P of the optical fibers F will notbe aligned in a straight line in a cross-section perpendicular to theoptical axes P. By making R≧Rmin*, however, even if Δ≦0, the amounts bywhich the optical axes P of the optical fibers F are shifted away fromthe straight line will become smaller. This amount of shift is relativeto the depth dimension of the optical fiber engagement portions C-1, butthe amount of shift in the positions of the optical axes P of theoptical fibers F relative to the direction of optical fiber alignmentwill also become smaller.

When R<Rmin*, the amount of shift in the optical axes P of the opticalfibers F will become larger, as will the optical connection loss whenthis optical fiber array is used. Moreover, when single mode fiber(having a core diameter φ=10 μm and an outer diameter 2RO=125 μm) isused for these optical fibers, it is possible to keep the opticalconnection loss between optical fiber arrays, or between an opticalfiber array and another component (such as when light waveguides havinga core diameter of φ are configured in an array) within 0.2 dB (aspecification deemed necessary in the fields of optical communicationsand measurement, etc.) by making Rmin**≦R≦Rmax (whereRmin**=Rmin-(φ/10).

    When θ>θc

If θ is within this range, then optical fiber crown exposure is possibleirrespective of the cross-sectional shape of the grindstone tip-(i.e.the cross-sectional shape of the bottom of the concavities in the mold),and there is no need to consider a minimum value for R in order to makecrown exposure possible. Accordingly, nothing is changed from before theexpansion.

The mold fabrication method described thus far, wherein a mold materialis machined by grinding with a grindstone having a cross-sectional shapeperpendicular to two main grinding surfaces that approximates thecross-sectional shape perpendicular to the optical axes of the opticalfibers when those optical fibers are engaged and arrayed in opticalfiber engagement portions in an optical fiber guide block, formingconcavities in prescribed positions and in a prescribed direction,affords advantages in that high-precision molds having shapes faithfulto their design can be fabricated with good reproducibility and goodproductivity.

The present invention is not limited to the fabrication of optical fiberguide blocks in which optical fiber engagement portions are arrayed at aconstant pitch. The invention may also be applied to an optical fiberguide block having but one optical fiber engagement portion. Forexample, two concavities such as are diagrammed in FIG. 8E may be formedat an interval of 2YO, and, if two-sided machining is performed, asdiagrammed in FIGS. 11A through 11C, a mold can be obtained forfabricating an optical fiber guide block having but one optical fiberengagement portion. Depending on the case, if a mold release thinfilm(s) is formed on the forming surfaces, and a material to be formingsuch as glass is press-formed, an optical fiber guide block having butone optical fiber engagement portion can be obtained. As is diagrammedin FIG. 8E, moreover, a plurality of concavities B-2 may be formed at apitch 2YO and made into a concavity group 1, and then a plurality ofconcavities B-2 formed at a different pitch 2YO' to make a concavitygroup 2, making forming surfaces that form optical fiber engagementportions between the concavity groups. In such case also, as expedient,if a mold release thin film(s) is formed on the forming surfaces, andglass or other material for forming is press-machined, it is possible toobtain an optical fiber guide block comprising a portion wherein opticalfibers are arrayed at a pitch interval of 2YO, and a portion whereinthey are arrayed at 2YO'.

Embodiment 1

A mold was fabricated for press-molding a glass preform, fabricating anoptical fiber guide block wherein are positioned and secured the opticalinput/output ends of single mode quartz glass fiber such as is widelyused in the fields of optical communications and optical measurement.The number of cores in the optical fibers engaged in the optical fiberengagement portions in the optical fiber guide block is 8, with a pitch2YO of 250 μm. The optical fiber radius is 62.5 μm. The parameterspertaining to the grindstone used in machining the concavities in themold for forming the optical fiber engagement portions in the opticalfiber guide block, and to the shape of the concavities, are listed inTable 1. Cross-sections of a mold corresponding to Table 1 arediagrammed in FIGS. 14A and 14B.

                                      TABLE 1                                     __________________________________________________________________________    Angle                                                                             Rmin                                                                             Rmax                                                                              dmin                                                                             dmax        Crown expos                                                                         Range for                                     θ (deg)                                                                     (μm)                                                                          (μm)                                                                           (μm)                                                                          (μm)                                                                           R (μm)                                                                         d (μ)                                                                          Δ (μm)                                                                     Δ (μm)                               __________________________________________________________________________    40  51.04                                                                            70.52                                                                             223.1                                                                            343.4                                                                             61.0                                                                              300 10    <37.47                                        50  42.22                                                                            75.42                                                                             182.6                                                                            268.0                                                                             52.2                                                                              240 10    <45.36                                        60  29.0                                                                             81.84                                                                             154.0                                                                            216.5                                                                             39.0                                                                              190 10    <52.83                                        70  9.49                                                                             90.1                                                                              132.0                                                                            178.5                                                                             19.5                                                                              150 10    <59.9                                         74  -- 94.02                                                                             124.5                                                                            165.8                                                                             19.5                                                                              140 13.3  <62.68                                        80  -- 100.68                                                                            114.2                                                                            148.9                                                                             19.5                                                                              130 21.5  <66.71                                        90  -- 114.28                                                                            99.1                                                                             125.0                                                                             19.5                                                                              110 33.9  <73.22                                        __________________________________________________________________________     Notes:                                                                        If the crownexposure amount Δ is first determined for angle θ     assuming constant pitch 2YO, R may be determined by the following equatio     for the range Rmin < R < Rmax.                                                Δ = R[{1/sin(θ/2)} - 1] - [{YO/tan(θ/2)} -                  {RO/sin(θ/2)} - RO] d is the depth of the intersection A4. The          actual grinding depth (depth of grindstone tip apex referenced against        mold material surface) will be the value obtained by subtracting the valu     of R[{1/sin(θ/2)} - 1] from d.                                          The "--" symbol in the Rmin column indicates that a positive value is         obtained for crown exposure if R < Rmax.                                 

In this embodiment, the cross-section of the concavities (grindstonecross-section) is V-shaped and the cross-section of the bottoms(grindstone tip cross-section) is shaped as a circular arc. The moldmaterial used was tungsten carbide. The grindstone used in grinding theconcavities was made of diamond grit. In Table 1, R is the radius ofcurvature of the circular arc and d is the depth of the concavities. Thesurface of the mold material machined was a flat surface. A dicing ofthe machine was used in grinding the concavities. In the surface of themold material, 9 concavities, that being the number of optical fibercores 8 plus 1, were formed, extending in the prescribed direction at apitch of 250 μm and parallel to one another. At this time, the positionsof the concavities in the mold material were adjusted so that a positionshifted by a half pitch YO, which is half the distance between thecenter of one concavity and the center of an adjacent concavity, formsthe center of an optical fiber engagement portion. Flat forming surfaceswere left remaining between the concavities in all of the molds, in ashape wherewith it is possible to form optical fiber guide blockscomprising optical fiber engagement portions having flat bottoms. Whenthe pitch YO and the optical fiber radius RO have the values notedabove, the boundary condition demanded for the shape of the grindstonetip is that angle θ be θc=74°. At angles exceeding 74°, molds can beobtained wherewith optical fiber crown exposure is possible irrespectiveof the cross-sectional shape of the grindstone tip.

After forming 9 concavities in this manner, a dicing machine was used toperform two-sided machining on the bottom of the outermost concavitiesand the ends of the portions removed by two-sided machining. After thetwo-sided machining, a mold release thin film(s) made of platinum wasformed on the forming surfaces to yield a mold equipped with moldrelease thin film(s).

Embodiment 2

Next, mold machining was performed using a grindstone having a flat tipshape. In Table 2 are listed parameters pertaining to the grindstone andto the mold concavities. Mold cross-sections corresponding to Table 2are presented in FIGS. 15A and 15B. In this figure, W is the width ofthe flat forming surface B-0-1 between the concavities B-2.

                  TABLE 2                                                         ______________________________________                                                                 Ground-                                                                       stone       Crown                                    Angle Rmin   dmin   dmax tip W       exposure                                                                             Range for                         θ (deg)                                                                       (μm)                                                                              (μm)                                                                              (μm)                                                                            (μm)                                                                             d (μm)                                                                           Δ (μm)                                                                      Δ (μm)                   ______________________________________                                        40    51.04  223.1  343.4                                                                              78.7  300   10     83.9                              50    42.22  182.6  268.0                                                                              63.1  240   10     88.9                              60    29.0   154.0  216.5                                                                              45.0  190   10     93.8                              70    9.49   132.0  178.5                                                                              24.0  150   10     98.3                              74    --     124.5  165.6                                                                              14.3  140   10     100.1                             80    --     114.2  148.9                                                                              10    130   16.7   102.7                             90    --     99.1   125.0                                                                              10    110   30.9   106.7                             ______________________________________                                         Notes:                                                                        The grindstone tip width W is determined using parameter R' that satisfie     the following formula.                                                        Δ = R'[{1/sin(θ/2)} - 1] - [{YO/tan(θ/2)} -                 {RO/sin(θ/2)} - RO]                                                     W = 2R' tan{( - θ)/4}                                              

When the pitch YO and the optical fiber radius RO have the values notedabove, the boundary condition demanded for the shape of the grindstonetip is that angle θ be θc=74°. At angles exceeding 74°, molds can beobtained wherewith optical fiber crown exposure is possible irrespectiveof the cross-sectional shape of the grindstone tip. This is the same asin Embodiment 1. Using such grindstone, concavity-grinding machining andtwo-sided machining were performed as in Embodiment 1. However, becausethe bottoms of the mold concavities are flat, the precision ofpositioning the ends of the portions removed by two-sided machining andthe bottoms of the outermost concavities was kept within the width ofthe flat bottoms. In this manner, shape machining was performed so asnot to make a mold having any unnecessary projections. The mold materialwas tungsten carbide. The grindstone used was made of the same substanceas in Embodiment 1. After the shape machining, a mold release thinfilm(s) made of platinum was formed on the forming surfaces of the moldto yield a mold equipped with mold release thin film(s).

Embodiment 3

Using the molds disclosed in Embodiments 1 and 2, an optical fiber guideblock C was formed, as depicted in FIG. 16, and an 8-core optical fiberarray was fabricated, as depicted in FIGS. 17A and 17B, using theoptical fiber guide block C and a pressure block M. In this embodiment,as diagrammed in FIGS. 18A through 18D, a mold D that forms a pedestalC-3 that carries an optical fiber sheath in the optical fiber guideblock C depicted in FIG. 16, and a mold B of the present invention,equipped with a mold release thin film(s) H. are integrated in asecuring frame E to form a down die, while, separately, a cavity Z wasconfigured, using trunk dies F to form the optical fiber guide blocksides, and an up die G to form the bottom of the optical fiber guideblock.

Glass preforms J having the compositions noted in Table 3 were placedinside the cavity Z, and, at the forming temperatures noted in Table 3,the glass preforms J were put under pressure by the up and down dies.

                                      TABLE 3                                     __________________________________________________________________________    Glass Composition*.sup.1                                                                SiO.sub.2                                                                             4.0 4.0 23.3                                                                              4.0 4.0 4.8 13.3                                          GeO.sub.2                                                                             --  5.0 --  --  --  --  --                                            B.sub.2 O.sub.3                                                                       27.2                                                                              32.2                                                                              22.2                                                                              32.2                                                                              37.2                                                                              32.2                                                                              32.2                                          ZnO     54.5                                                                              40.5                                                                              42.5                                                                              40.5                                                                              40.2                                                                              40.7                                                                              44.0                                          MgO     --  --  --  --  --  --  1.0                                           CaO     --  --  --  --  --  --  1.5                                           SrO     --  --  --  --  --  --  --                                            BaO     --  --  --  --  --  --  --                                            PbO     --  --  --  --  --  --  --                                            (A)*.sup.2                                                                            54.5                                                                              40.5                                                                              42.5                                                                              40.5                                                                              40.2                                                                              40.7                                                                              46.5                                          Al.sub.2 O.sub.3                                                                      2.5 1.0 7.5 1.0 2.5 9.0 5.5                                           (B)*.sup.3                                                                            88.2                                                                              82.7                                                                              95.5                                                                              77.7                                                                              82.4                                                                              86.7                                                                              97.5                                          Li.sub.2 O                                                                            2.5 2.5 4.5 2.5 --  2.5 2.5                                           La.sub.2 O                                                                            9.3 13.3                                                                              --  13.3                                                                              15.3                                                                              4.3 --                                            Y.sub.2 O.sub.3                                                                       --  --  --  5.0 --  --  --                                            TiO.sub.2                                                                             --  --  --  --  0.4 --  --                                            ZrO.sub.2                                                                             --  1.5 --  1.5 1.5 1.5 --                                            Nb.sub.2 O.sub.5                                                                      --  --  --  --  0.4 --  --                                            Ta.sub.2 O.sub.5                                                                      --  --  --  --  --  5.0 --                                            Sb.sub.2 O.sub.3 *.sup.4                                                              --  --  0.5 --  --  --  --                                  Parameter Transition point                                                                      465° C.                                                                    500° C.                                                                    470° C.                                                                    500° C.                                                                    530° C.                                                                    510° C.                                                                    495° C.                                Yield point                                                                           495° C.                                                                    540° C.                                                                    500° C.                                                                    530° C.                                                                    555° C.                                                                    540° C.                                                                    520° C.                                Mean CTE*.sup.5                                                                       64  63  62  66  67  64  66                                            UV Perm.*.sup.6                                                                       81% 85% 91% 84% 80% 81% 83%                                 Forming temp      545° C.                                                                    593° C.                                                                    553° C.                                                                    584° C.                                                                    595° C.                                                                    592° C.                                                                    573° C.                      __________________________________________________________________________     *.sup.1 Values for each component are in values of wt %.                      *.sup.2 Represents Zno, MgO, CaO, SrO, BaO, and PbO total content.            *.sup.3 Represents SiO.sub.2, GeO.sub.2, B.sub.2 O.sub.3, RO (R = Zn, Mg,     Ca, Sr, Ba, Pb), and Al.sub.2 O.sub.3 total content.                          *.sup.4 Represents amount added outside composition proportions.              *.sup.5 Represents mean coefficient of thermal expansion from room            temperature to 400° C., in ×10.sup.-7 /° C. units.        *.sup.6 Represents transmissivity of UV radiation of 350 nm wavelength        through a test piece 2 mm in thickness.                                  

After sufficient glass packing, the molding K was removed from the dieto yield an optical fiber guide block C. Into the optical fiberengagement portions C-1 of the optical fiber guide block C fabricated asnoted above, 8 quartz-glass single mode fibers were engaged and secured,as diagrammed in FIGS. 17A and 17B. Then, with the optical fiber sheathmounted on the pedestal C-3, a UV-hardening adhesive was applied, andthe optical fiber sides were pressed down with a glass pressure block Mhaving a flat pressing surface M-1. The adhesive was then irradiatedwith UV rays through the glass, thereby hardening the adhesive andsetting the optical fibers. The light input/output end surfaces of theoptical fiber array fabricated in this manner were optically polished tocomplete the optical fiber array.

After this polishing, the vicinity of the secured optical fibers sosecured was examined under an electron microscope, from the endsurfaces. This confirmed that all eight of the optical fibers weresupported at three points. The optical fiber array was then subjected toa thermal cycle in which it was found that the total optical-connectionloss fluctuation amplitude was within 0.3 dB. No changes in the locationaccuracy of the optical fibers were observed after these tests, nor wereseen any changes in the condition wherein the optical fibers were heldand secured by three-point support. When materials other than tungstencarbide, as noted above, were used as the mold material, the same goodresults were obtained. Thus, by employing the present invention, opticalfiber crown exposure can be effected, making it possible to secure theends of optical fibers by three-point support, and thereby enablingoptical fibers to be stably held and secured with high locationaccuracy.

If the radius of the imaginary circle that forms the minimum radius ofcurvature of concavities shaped as circular arcs in a mold is within theexpanded range, as provided, it is possible to effect stable holding andsecuring at high location accuracy, even without employing three-pointsupport, and to keep the optical-connection loss in an optical fiberarray within allowable limits.

What is claimed is:
 1. A mold for fabricating optical fiber guideblocks, for the purpose of molding, by press-molding process, at leastthe optical fiber engagement portions of optical fiber guide blockscomprising optical fiber engagement portions for the purpose ofpositioning and aligning optical fibers at a fixed pitch; comprising:aplurality of concavities that extend in one direction in the formingsurface; wherein the tangent lines at the points where the portions thatare to support said optical fibers at the two sloping surfaces whichconfigure said concavities, in a cross-section that is perpendicular tothe longitudinal dimension of said concavities, subtend an angle θ thatis equal to or smaller than θc which satisfies the relationship notedbelow; the perpendicular cross-sectional shape of said concavities issuch that the contour thereof is contained within an area bounded by twotangent lines that touch the sloping surfaces and by a line that istangent to an imaginary circle and perpendicular to the straight lineconnecting the intersection of said two tangent lines with the center ofsaid imaginary circle, and that passes between said intersection andsaid center of said imaginary circle, when said imaginary circle, ofradius Rmin as defined below, is inscribed in the area that is in thebight of said two tangent lines; the depth of said concavities is suchthat said intersection of said two tangent lines is at a position deeperthan dmin, as defined below; and said forming surfaces between saidconcavities are what form said optical fiber engagement portions:

    θc=2 tan.sup.-1 {S.sup.2 -1)/2S},

where:S=YO/RO;

    Rmin=[RO+{RO/sin(θ/2)}-{YO/tan (θ/2)}]/[1-{1/sin(θ/2)}];

    dmin=[YO-RO·tan{(π-θ)/4}]/tan(θ/2);

RO is the optical fiber radius; and YO is half the pitch length of theoptical fiber engagement portion.
 2. The mold for fabricating opticalfiber guide blocks, according to claim 1, wherein the cross-sectionalshapes perpendicular to the longitudinal dimension of a plurality ofconcavities are the same.
 3. A mold for fabricating optical fiber guideblocks, for the purpose of molding, by press-molding process, at leastthe optical fiber engagement portions of an optical fiber guide blockthat comprises groove-shaped optical fiber engagement portions for thepurpose of positioning optical fibers; comprising:convexities thatextend in the longitudinal dimension of the forming surface; andconcavities that extend in the longitudinal dimension, arrayed with saidconvexities sandwiched in between them; wherein the tangent lines at thepoints where are formed the portions of the two sloping surfaces thatconfigure said concavities in a cross-section perpendicular to thelongitudinal dimension of said concavities, which portions are tosupport said optical fibers, subtend an angle θ that is equal to orsmaller than θc which satisfies the relationship noted below; theperpendicular cross-sectional shape of said concavities is such that thecontour thereof is contained within an area bounded by the two tangentlines that touch said sloping surfaces and by a line that is tangent toan imaginary circle and perpendicular to the straight line connectingthe intersection of said two tangent lines with the center of saidimaginary circle, and that passes between said intersection and saidcenter of said imaginary circle, when said imaginary circle, of radiusRmin as defined below, is inscribed in the area that is in the bight ofsaid two tangent lines; the depth of said concavities is such that saidintersection of said two tangent lines is at a position deeper thandmin, as defined below; and one or other of said sloping surfaces thatform said concavities is what forms the surfaces that support saidoptical fibers in said optical fiber engagement portions:

    θc=2 tan.sup.-1 {S.sup.2 -1)/2S},

where:S=YO/RO;

    Rmin=[RO+{RO/sin(θ/2)}-{YO/tan (θ/2)}]/[1-{1/sin(θ/2)}];

    dmin=[YO-RO·tan{(π-θ)/4}]/tan(θ/2);

RO is the optical fiber radius; and 2YO is the interval between theconcavities arrayed so as to sandwich the convexities between them. 4.The mold for fabricating optical fiber guide blocks, according to claim3, wherein the cross-sectional shapes perpendicular to the longitudinaldimension of said concavities are the same.
 5. The mold for fabricatingoptical fiber guide blocks, according to claims 1, wherein Rmin*, whichsatisfies the relationship noted below, applies instead of Rmin:

    Rmin*=Rmin-(φ/5),

where:φ is the optical fiber core diameter.
 6. A mold for fabricatingoptical fiber guide blocks, for the purpose of molding, by press-moldingprocess, at least the optical fiber engagement portions of an opticalfiber guide block comprising optical fiber engagement portions for thepurpose of positioning and aligning optical fibers at a fixed pitch;comprising:a plurality of concavities that extend in one direction inthe forming surface; wherein the tangent lines at the points where theportions that are to support said optical fibers at the two slopingsurfaces which configure the concavities, in a cross-section that isperpendicular to the longitudinal dimension of said concavities, subtendan angle θ that exceeds θc which satisfies the relationship noted below;the depth of said concavities is such that said intersection of saidtangent lines is at a position deeper than dmin, as defined below; andthe forming surfaces between said concavities are what form said opticalfiber engagement portions:

    θc=2 tan.sup.-1 {S.sup.2 -1)/2S},

where:S=YO/RO;

    dmin=[YO-RO·tan{(π-θ)/4}]/tan(θ/2);

RO is the optical fiber radius; and YO is half the pitch length of theoptical fiber engagement portion.
 7. The mold for fabricating opticalfiber guide blocks, according to claim 6, wherein the cross-sectionalshapes perpendicular to the longitudinal dimension of a plurality ofconcavities are the same.
 8. A mold for fabricating optical fiber guideblocks, for the purpose of molding, by press-molding process, at leastthe optical fiber engagement portions of an optical fiber guide blockthat comprises groove-shaped optical fiber engagement portions for thepurpose of positioning and supporting optical fibers;comprising:convexities that extend in the longitudinal dimension of theforming surface; and concavities that extend in the longitudinaldimension, arrayed with the convexities sandwiched in between them;wherein the tangent lines at the points where are formed the portions ofthe two sloping surfaces that configure said concavities in across-section perpendicular to the longitudinal dimension of saidconcavities, which portions are to support said optical fibers, subtendan angle θ that exceeds θc which satisfies the relationship noted below;the depth of said concavities is such that the intersection of saidtangent lines is at a position deeper than dmin, as defined below; andone or other of the sloping surfaces that form the concavities is whatforms the surfaces that support said optical fibers in the optical fiberengagement portions:

    θc=2tan.sup.-1 {S.sup.2 -1)/2S},

where:S=YO/RO;

    dmin=[YO-RO·tan{(π-θ)/4}]/tan(θ/2);

RO is the optical fiber radius; and 2YO is the interval between theconcavities arrayed so as to sandwich the convexities between them. 9.The mold for fabricating optical fiber guide blocks, according to claim8, wherein each of the cross-sectional shapes perpendicular to thelongitudinal dimension of said concavities is identical with oneanother.
 10. The mold for fabricating optical fiber guide blocks,according to claim 1, wherein the shapes of the bottoms of saidconcavities in a cross-section perpendicular to the longitudinaldimension of said concavities are arcuate in configuration.
 11. The moldfor fabricating optical fiber guide blocks, according to claim 1,wherein the bottoms of said concavities are flat.
 12. The mold forfabricating optical fiber guide blocks, according to claim 1 comprising:a plurality of concavities, wherein the forming surfaces bounded betweensaid concavities are flat; and said flat surfaces are positioned in thesame plane.
 13. The mold for fabricating optical fiber guide blocks,according to claim 1, comprising: a mold release thin film(s), at leaston the forming surfaces.
 14. A method of fabricating optical fiber guideblocks wherein a mold for fabricating optical fiber guide blocks,according to claim 1 is used; andthe raw material to be molded ispress-molded under heat.
 15. The mold for fabricating optical fiberguide blocks, according to claim 3, wherein Rmin*, which satisfies therelationship noted below, applies instead of Rmin:

    Rmin*=Rmin-(φ/5),

where:φ is the optical fiber core diameter.
 16. The mold for fabricatingoptical fiber guide blocks, according to claim 3, wherein the shapes ofthe bottoms of said concavities in a cross-section perpendicular to thelongitudinal dimension of said concavities are arcuate in configuration.17. The mold for fabricating optical fiber guide blocks, according toclaim 6, wherein the shapes of the bottoms of said concavities in across-section perpendicular to the longitudinal dimension of saidconcavities are arcuate in configuration.
 18. The mold for fabricatingoptical fiber guide blocks, according to claim 8, wherein the shapes ofthe bottoms of said concavities in a cross-section perpendicular to thelongitudinal dimension of said concavities are arcuate in configuration.19. The mold for fabricating optical fiber guide blocks, according toclaim 3, wherein the bottoms of said concavities are flat.
 20. The moldfor fabricating optical fiber guide blocks, according to claim 6,wherein the bottoms of said concavities are flat.
 21. The mold forfabricating optical fiber guide blocks, according to claim 8, whereinthe bottoms of said concavities are flat.
 22. The mold for fabricatingoptical fiber guide blocks, according to claim 3 comprising:a pluralityof concavities, wherein the forming surfaces bounded between saidconcavities are flat; and said flat surfaces are positioned in the sameplane.
 23. The mold for fabricating optical fiber guide blocks,according to claim 6 comprising:a plurality of concavities, wherein theforming surfaces bounded between said concavities are flat; and saidflat surfaces are positioned in the same plane.
 24. The mold forfabricating optical fiber guide blocks, according to claim 8comprising:a plurality of concavities, wherein the forming surfacesbounded between said concavities are flat; and said flat surfaces arepositioned in the same plane.
 25. The mold for fabricating optical fiberguide blocks, according to claim 3 comprising:a mold release thinfilm(s), at least on the forming surfaces.
 26. The mold for fabricatingoptical fiber guide blocks, according to claim 6 comprising:a moldrelease thin film(s), at least on the forming surfaces.
 27. The mold forfabricating optical fiber guide blocks, according to claim 8comprising:a mold release thin film(s), at least on the formingsurfaces.